1. Field of the Invention
The present invention generally relates to a capacitive button device and, more particularly, to a capacitive button device capable of improving the resolution of capacitive buttons.
2. Description of the Prior Art
Please refer to FIG. 1 and FIG. 2, wherein FIG. 1 is a block diagram of a conventional capacitive button device and FIG. 2 shows how the signal changes when a conventional capacitive button device is touched. When a finger touches a printed circuit board (PCB) or a glass substrate 2 during a signal transmission process conducted by a signal transmitting device 1, part of the transmitted charges are introduced through the finger, while the other charges are transmitted in two paths. In one path, the charges are directly coupled to the integrating and amplifying device 3; and in the other path, the charges are radiated into the air. The charges coupled to the integrating and amplifying device 3 generate a permanent base for the button device. The permanent base is about 80% to 90% of the untouched coupled potential. In other words, the change is only 10% to 20% after the capacitive touch device is touched. Meanwhile, only 10% to 20% of the bit order can be effectively used after the signal is processed by a digital-to-analog converting unit.
In the conventional capacitive button device, the transmitted signal is coupled to the integrating and amplifying device 3 through an equivalent capacitance formed by the PCB or the glass substrate 2 before it is converted by an analog-to-digital converting unit 4 into a digital data to be stored in a data storage unit 5. The digital data is then output and identified by a data output unit 6. When a capacitive button is touched, part of the charges in the integrated signal are introduced through the finger that touched the capacitive button so that the potential of the integrated signal drops. The charges introduced through the finger cause the potential to drop by 10% to 20%, while the remained 80% to 90% of the signal processed by the analog-to-digital converting unit 4 will not change. The resolution of touch response is only 10% to 20% of the analog-to-digital converting unit 4. Therefore, if the analog-to-digital converting unit 4 is be to used, the permanent base, which is 80% to 90% of the signal, has to be deducted so that only the change of the signal is processed by the analog-to-digital converting unit 4 to improve the resolution.
Accordingly, the conventional capacitive button device is problematic in:
1. poor resolution of the buttons;
2. large hardware size and high manufacturing cost; and
3. restriction in use for general control buttons only.
Therefore, there exists a need in providing a capacitive button device capable of improving the resolution of conventional capacitive buttons and being used with touch panels to downsize the digital-to-analog converting unit with improved resolution and reduced cost in design and fabrication.